1. Field:
The present invention relates to a high-voltage thyristor converter for use in DC power transmission or the like.
2. Prior Art:
FIG. 1 is a connection diagram of a high-voltage thyristor converter to which the present invention is to be applied, wherein an alternating current supplied from AC buses R, S and T is converted into a direct current via bridge-connected valves U-Z or a direct current from DC buses P and N is converted into an alternating current.
Each of the valves U-Z constituting the high-voltage converter is assembled as illustrated in FIG. 3 by superposing a desired number of thyristor modules SM on one another by the use of insulator pillars B, each thyristor module SM comprising, as illustrated in FIG. 2, a plurality of thyristor elements Sl-Sn and accessory components such as an anode reactor AL, resistors and capacitors.
In transferring a gate signal to individual thyristor elements constituting a thyristor module SM, there is known a mode which transfers to a high-voltage section an electric signal converted by means of a pulse transformer at a ground potential, and a mode which converts an operation command into a light signal by a transducer at a ground potential and then transfers the light signal to a high-voltage section via a light guide LG such as an optical cable as illustrated in the example of FIG. 3.
FIG. 4 shows the principle of a gate signal transfer system employing optical cables, wherein a transducer 1 for converting a thyristor-valve operation command into a light signal is equipped internally with light emitting elements EL. There are also shown a light guide LG composed normally of an optical cable and serving to transfer the output signal of the light emitting element EL to a thyristor module SM at a high voltage level; a joint JT disposed between the thyristor module SM and the light guide LG and so formed as to be detachable by the use of a coupler; and a light sensitive element LE for converting an input into an electric signal which serves as a trigger signal to drive a thyristor ET.
Meanwhile, due to the service life of electric circuit components constituting the thyristor module SM, it is necessary to replace each thyristor module with a new one after the lapse of a predetermined term. In such replacement where a joint JT needs to be attached to or detached from the thyristor module SM for connection of the cable to transfer electric or light signal, it has been unavoidable that some damage is caused to the light guide LG. Particularly the optical cable for transfer of light signal has a relatively low flexibility and is therefore prone to be broken during the work of replacement. Furthermore, in an UHV-class thyristor valve employed in a 500 kV DC transmission system, the withstand voltage characteristic of the optical cable is inferior to that of an epoxy cast product or the like, so that some proper improvement has been required in this aspect as well.